Process of developing photographic pictures



Patented A r. 21, 1942 PROCESS OF DEVELOPING PHOTOGRAPHIC PICTURESAndreas Schilling and Wilhelm Schneider,

Dessau, and Gustav Wilmanns, Woli'en, Kreis Bitterleld, Germany,assignors, by mesne assignments, to General Aniline & Film Corporation,New York, N. Y., a corporation of Delaware No Drawing. ApplicationNovember 14, 1939, Se rial No. 304,321. In Germany November 24,

3 Claims. (CI. 95-88) This invention relates to a process of developingphotographic pictures and more particularly to the step of stopping theaction of a photographic developer.

In ordinary black and white developing as well as in color-formingdevelopment the developer still acts on the photographic material whenthe same has been taken out of the developing bath and inserted into thesubsequent washing bath. In the usual black and white development thisfeature is of no special consequence since only a certain increase indeveloped silver occurs, which may be recognized by a more intenseblackening of the picture; the action of the developer subsequently tothe development step proper is extremely undesirable in the processofcolorforming development since it may easily cause a shifting of thecolor shades, that is a falsification of the color values, which iscaused especially by the fact that the lower layers of a multi-layerphotographic element are more intensely developed than the top layers.of the color shades it is to be expected that under certaincircumstances the ratio of gradation between the several layers isdisturbed. In black and white development it has been usual to preventthis subsequent action of the developer by inserting in between thedevelopment and the fixing baths .a stopping bath. These stopping bathswere in general composed of dilute acids which neutralize the alkali ofthe developer and thereby interrupt the development of the silverhalide.

In color-forming development the employment of such dilute acids asstopping baths is impossible since very dilute acids already act on thedyes formed by color-forming development. For instance the bluequinoneimine dyes are transformed into the red dyestufi salts by theacids and are partly completely destroyed- It has been found that thedegree of acid which acts no longer on the dyes obtained bycolor-forming development is round about a pH-value higher This pH-valuecorresponds to very.

than 3. dilute acetic acid. If such very dilute acid so- Y lutionshaving a pH-value higher than 3 were employed for stopping thedevelopment it would be necessary to use so very dilute solutions thattheir stopping action would rapidly be neutralized by the alkali of the.developer contained in the photographic layers. Furthermore, very weakacids do not yield water-resistant salts with the color-formingdeveloper. Such stable salts, however, are necessary, since not only theaction Besides this shifting developer must be dissolved from the layersin the form of a salt, it being known that the free base ofdimethylamino-aniline, the usual colorformingdeveloper, is ratherdifficulty soluble.

It is an object of the invention to overcome the above discusseddiiiiculties.

A further object of the invention consists in the provision of animprovement in the color- A further object of the invention is toprovide a novel photographic stopping bath.

Further objects of the invention will become apparent from the detailedspecification following hereinafter.

We have found that the after-effects of the color-forming developer maybe neutralized and the disadvantages of the stopping bath hitherto inuse may at the same time be avoided, by employing as stopping bathssolutions of primary or secondary salts polybasic organic acids the pH-value of which is not lower than 3 in solution. Advantageously apH-value of between 3 and 5 is selected. It is known that the pH-valueof such salt solutions which are known as buffer solutions areindependent of the concentration employed and it is therefore possibleto employ solutions of high concentration or saturated solutions.

The stopping baths according to the present invention therefore act withvery high ef- 'ficiency and-the effect of stopping the developer isproduced rapidly and with certainty. Furthermore, the above describeddamaging of the dyes is avoided and the color-forming developmentcompound is transformed into an easily soluble form as a mixed salt andcan easily be washed out of the layer.

The stopping baths may be employed in the color-forming developmentoflayers containing Example A multi-layer photographic element containingdyestufl components fast to diffusion is developed by color-formingdevelopment. At the end of the alkali must be DDed but the -f mingthecolorr-forming development it is immediately per cent of primarysodium citrate. After being treated in the stopping bath for 1 minutethe iiim is watered, bleached and fixed.

we claim:

1. In a process of producing color photographic pictures bycolor-forming development the step which comprises immersing the colorphotographic element immediately after the development thereof in astopping bath containing a buffer solution of an acidic salt of apolybasic organic acid the pH-value of a solution of said salt beinghigher than 3. v

2. In a process of producing color photographic pictures bycolor-forming development the step which comprises immersing the colorphotographic element immediately after the development thereof in astepping bath containing a bufler solution 0! an acidic salt of apolybasic organic acid the pH-value of a solution of said salt beingfrom 3 to 5.

3. In a. process of producing color photographic pictures bycolor-forming development the step which comprises immersing the colorphotographic element immediately after the development thereof in asolution containing aboutlO. per cent of primary sodium citrate.

ANDREAS SCHILLING, WILHELM SCHNEIDER, GUSTAV WIIMANNS.

